“…4) we found that when the concentration of alkali changes in the titration, at the same time a sharp change in pH occurs, as well as a sharp change in the position of maximum reflection and a sharp and significant (almost by an order of magnitude) change in the diffraction efficiency of the holographic sensor. This indicates a significant change of the optical characteristics of the holographic layer [28,33]. These characteristics include diffraction effectivity (DE), transmission, spectral form of the reflection line (in particular, its width) and wavelength distribution over the hologram surface.…”